Abstract
Continuous-wave, time-integrated, and time-resolved photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO/Zn0.78Mg0.22O quantum wells of varying widths. By comparing experimental results with a variational calculation of excitonic energies and oscillator strengths, we determine the magnitude (0.9MV∕cm) of the longitudinal electric field that is induced by both spontaneous and piezoelectric polarizations. The quantum-confined Stark effect counteracts quantum confinement effects for well widths larger than 3nm, leading to emission energies that can lie 0.5eV below the ZnO excitonic gap and to radiative lifetimes that can be larger than milliseconds.